(1) Field of the Invention
This invention relates to a non-aqueous secondary cell having lithium or lithium alloy as an active material of a negative electrode, especially to an improved positive electrode.
(2) Description of the Related Art
As an active material of a positive electrode of a non-aqueous secondary cell, molybdenum trioxide, vanadium pentoxide, sulfide of titanium or niobium, activated carbon, and the like have been proposed, and some of them have been put into practical use.
As an active material of a positive electrode of a non-aqueous primary cell, manganese dioxide (MnO.sub.2) and carbon fluoride are well known and have already been practically used. Especially, MnO.sub.2 has advantages of excellent storage characteristics, availability in abundance and low cost.
MnO.sub.2 is considered to be suitable for an active material of a positive electrode of a non-aqueous secondary cell because of the above reasons. However, it is poor in reversibility, which results in a poor charge/discharge cycle characteristic.
In order to solve the above problem of MnO.sub.2, the applicant proposed using MnO.sub.2 including Li.sub.2 MnO.sub.3 as an active material of a positive electrode (U.S. Pat. No. 4,758,484). This improved the charge/discharge cycle characteristic to some extent, but more improvement has been demanded for practical use.
As for an active material of a positive electrode of a non-aqueous primary cell, Japanese Patent Kokai No. 56-57260 discloses the use of a compound obtained by heat-treating a mixture of MnO.sub.2 and MoO.sub.3 (molybdenum trioxide). It is known that this compound improves the discharge characteristic in the high rate range because of its distorted crystal structure. However, when the compound is used for a secondary cell, the distortion is not big enough to improve the charge/discharge reversibility of the cell.